Method And Apparatus For Manufacturing Lead Frames

Abstract

Lead frames having plate-like heat sink portion and three leads, one of which is integral with heat sink, are manufactured by blanking heat sink and leads, bending the integral lead relative to the heat sink, forming ends of the remaining leads, and again bending integral leads so that leads are in a plane which is parallel to, and spaced from, the heat sink.

Description

BACKGROUND OF THE INVENTION

A known type of transistor lead frame shown in the Patent to Tascovich U.S. Pat. No. 3,597,666, comprises a relatively massive heat sink, on which the transistor or chip is mounted, and three leads which are disposed in a plane extending parallel to, and spaced from, the heat sink. The center lead is connected to the heat sink and the ends leads have their end portions extending over the surface of the heat sink and are reversely bent towards each other so that their tips lie between the two planes. The transistor is disposed beneath the tip portions of the outside leads and these tips are bonded to the contact portions of the chip, the center lead serving as a collector for the transistor.

Lead frames of the type described above required leads of relatively thin stock metal. They also require a relatively thick heat sink to provide the required heat dissipation ability. Because of this fact, and because of the relative complexity of this type of lead frame, it has been customary in the past to manufacture such lead frames from two separate strips which are subsequently assembled to each other. The heat sinks are manufactured by stamping a relatively thick metal strip and the leads are manufactured by stamping and forming a relatively thin strip. The collector lead, in accordance with prior art practice, may then be assembled to the heat sink by a clinching or other mechanical fastening operation.

The instant invention is directed to the achievement of a one piece transistor lead frame having a relatively thick platelike heat sink section and three leads which are intricately formed in spaced relationship to the heat sink. It is accordingly an object of the invention to provide an improved method and apparatus for manufacturing transistor lead frames. It is a further object to provide a method and apparatus for manufacturing lead frames having a heat sink and having intricately formed leads in the form of a continuous strip. It is a further object to provide an improved stamping and forming die for the manufacture of lead frames. It is a further object to provide a method and apparatus for carrying out stamping, bending, and forming operations on a metal strip to produce a lead frame having two metal thicknesses and having intricately formed lead ends. A still further object is the achievement of a lead frame having pre-applied solder on its heat sink portion and on the ends of its contact arms.

These and other objects of the invention are achieved in a preferred embodiment thereof which is briefly described in the foregoing abstract, which is described in detail below, and which is illustrated in the accompanying drawings in which:

FIG. 1 is a perspective view of a stamping and forming die in accordance with the invention for producing lead frames in strip form in accordance with the method of the invention.

FIG. 2 is a plane view of the forming die of FIG. 1 with portions of the upper die shoe broken away to reveal portions of the tooling in the lower die shoe.

FIGS. 3A and 3B are plan views of a strip progression produced by the progressive die of FIG. 1, this view illustrating the successive stages in the formation of lead frames in accordance with the invention; FIGS. 3A and 3B are adapted to be placed beside each other to show the complete progression.

FIG. 3C is a perspective view of a short section of lead frame strip in accordance with the invention.

FIG. 3D is a perspective view of a short section of heat metal stock of the type used to produce lead frames in accordance with the invention.

FIG. 4 is a plane view on an enlarged scale of the tooling in the lower die shoe for initially bending the ends of the outside leads downwardly.

FIG. 5 is a view taken along the lines 5--5 of FIG. 4.

FIG. 6 is a view taken along the lines 6--6 of FIG. 4 showing the positions of the lower and upper tooling prior to the initial bending and forming operations which are performed on the contact arms.

FIG. 7 is a view similar to FIG. 6 but showing the positions of the parts when the upper tooling has been moved downwardly into engagement with the lower tooling and after the bending and forming operations have been carried out.

FIG. 8 is a sectional view taken along the lines 8--8 of FIG. 2 illustrating the tooling at the first bending station of the die in which all of the leads are bent downwardly from their original planes.

FIG. 9 is a view similar to FIG. 8 but showing the positions of the parts after the initial lead bending operation has been carried out.

FIG. 10 is a view taken along the lines 10--10 of FIG. 2 showing the upper and lower tooling for further forming the contact arms on the ends of the outside leads.

FIG. 11 is a view similar to FIG. 10 but showing the positions of the parts at the conclusion of this arm forming operation.

FIG. 12 is a view taken along the lines 12--12 of FIG. 10.

FIG. 13 is a view taken along the lines 13--13 of FIG. 11.

FIG. 14 is a view taken along the lines 14--14 of FIG. 2 showing the station at which the leads are bent back into a plane parallel to the plane of the heat sink.

FIG. 15 is a view similar to FIG. 14 but showing the positions of the parts at the conclusion of this second bending operation.

FIG. 16 is a view taken along the lines 16--16 of FIG. 15.

FIG. 16A is a fragmentary perspective view of an upper bending tool shown in FIG. 16.

FIG. 17 is a view taken along the lines 17--17 of FIG. 2 and showing a forming station at which the connecting strap, which extends between the collector lead and the heat sink is bent to position the outside leads centrally above the heat sink.

FIG. 18 is a view similar to FIG. 17 but showing the positions of the parts at the conclusion of this connecting strip forming operation.

FIG. 19 is a view taken along the lines 19--19 of FIG. 2 illustrating the tooling which is provided at a final sizing and forming station.

FIG. 20 is a view similar to FIG. 19 but showing the positions of the parts after the final sizing and forming operation has been carried out.

FIG. 21 is a view taken along the lines 21--21 of FIG. 20.

Referring first to FIG. 3C, a typical transistor lead frame 2 of the type adapted to be produced in accordance with the method of, and by a stamping and forming die in accordance with, the instant invention comprises a relatively thick and massive metallic heat sink 4 having three leads 6, 8, 10 associated therewith. These leads are disposed in a plane which extends parallel to, and is spaced from, the plane of the heat sink 4, the center lead 8 being reversely bent at its inner end 13 and including a reversely extending connecting strap portion 12 which is integral with one edge 14 of heat sink 4 as indicated at 15. The outside leads 6, 10 have end portions 18 which extend over the upper surface of the heat sink 4 and past the edge 14. These outside leads have contact arms 20 on their ends which extend laterally in opposite directions and which are reversely bent downwardly towards the heat sink and inwardly towards each other so that the tips 24 of these arms are disposed in front of the connecting strap 12 and immediately above the surface of the heat sink. It should be noted at this point that these arm tips 24 are spaced apart by a distance which is substantially less than the width of the connecting strip 12 of center lead 8. This spacing is relatively critical for the reason that the tips of these contact arms will be bonded, to the contact areas of the chip which is mounted on the heat sink. The outer arms 6, 10 are not directly connected to the heat sink 4 but are integral with the center lead 8 by virtue of the presence of a transversely extending tie bar 16.

When a transistor is assembled to the frame 2, the transistor or chip is placed on the upper surface of heat sink 4 with the tip portions 24 of the contact arms disposed against the contact areas of the chip. The chip has a thickness which is somewhat greater than the spacing between the ends 24 of the arms and the surface of the heat sink so that the chip is resiliently held in position while the frame is passed through a furnace in which solder metal 26 on the surface of the heat sink is reflowed to secure the chip to the frame. Thereafter, the ends of the leads, the chip, and portions of the heat sink are encapsulated by a molding process, the tie bar 16 functioning as a mold closure or dam bar during molding. The portions of the tie bar which extend between the leads are then removed by a stamping operation so that they are electrically separated from each other.

Turning now to FIGS. 3A, 3B, and 3D the method aspect of the invention is illustrated by the progression which shows the successive stamping and forming steps performed on strip metal to produce the finished lead frame. The strip metal stock 30, FIG. 3D, has a relatively thick section 32 and a relatively thin section 34 with a preapplied solder stripe on the surface of the thick section and adjacent portions of the thin section. Stock metal of this type may be produced by rolling or milling metal strip having a uniform thickness. Frames in accordance with the invention are conventionally produced from copper alloy stock which has been plated with nickel although other metals may be used.

As the stock metal passes through the die 48, which is described below, pilot holes 36, 38 are first punched and a generally rectangular opening 39 is formed in the thin stock section 34 in overlapping relationship to the edge of the solder stripe 26. Thereafter, an elongated opening 40 is punched beside each of the openings or holes 39, this opening 40 having a laterally extending recess intermediate its ends. The leads are initially formed by punching the upper edge, as viewed in the drawing, of the thin stock section and relatively thin slits 42 are then punched on each side of each opening 39 as shown at the location indicated at 41. The operation of punching these narrow openings or slits 42 defines the connecting strip portion 12' of the incipient lead frames and the contact arms 20' of two adjacent frames are formed when a short section of the stock between two adjacent frames is removed. The leads 6, 8, 10 are then stamped so that they have a generally U-shaped cross section as shown at 62. Subsequently at 43, FIG. 3A, the contact arms 20' are bent downwardly and, as will be explained below, partially inwardly towards each other. However, the spacing between the tips of the arms at this stage is greater than the width of the connecting strap portions 12' of the incipient frames.

Subsequently, some conventional punching and coining operations are carried out to remove stock metal between adjacent lead frames and to coin and finally form the sides of the heat sinks.

At location 44, the connecting strap section 12 of the center lead is bent at a location 13 which is remote from the heat sink so that all of the leads now extend normally of the plane of the stock metal. During such bending, the partially formed ends of the outside leads 6, 10 are swung along an arcuate path past the edges of the connecting section 12 of the center lead so that the contact arms are now above the surface of the connecting strap 12 of the center lead. These contact arms can now be formed inwardly until they are spaced apart by the required precisely predetermined distance which is less than the width of the connecting strap.

At location 46, the connecting strap section 12 is bent at 15 adjacent to edge 4 of the heat sink so that the leads are swung along an arcuate path until they are disposed above the plane of the heat sink and the connecting strap is then further formed or bent until it extends reversely between the planes defined by the heat sink and the leads. A final sizing and forming operation may be carried out to precisely locate the leads relative to the heat sink.

Turning now to FIGS. 1 and 2, a preferred form of stamping and forming die 48 in accordance with the invention comprises an upper die shoe 50, a lower die shoe 52 and guides 54 which guide the upper shoe towards the lower shoe. A die set of the type shown at 48 is adapted to be placed in a conventional punch press in accordance with conventional stamping and forming techniques and contains lower and upper tooling 58, 60 which progressively forms strip metal stock as it moves therethrough. The lower tooling 56 is mounted in a channel-shaped depression 58 extending the length of the die and in other recesses more fully described below and the upper tooling 60 is similarly mounted in the upper die shoe.

As shown in FIG. 2, the lower die tooling is mounted in separate blocks in the lower die but a generally channel-shaped depression 62 is provided which extends for the full length of the die and through which the heat sink portions 4 of the strip are fed. The leads 6, 8, 10 extend downwardly as viewed in FIG. 2 towards the front portion 74 of the lower die shoe so that they are carried past the forming stations.

The initial punching operations in which the openings 36, 38, 39, 40 and 42 are formed are now shown inasmuch as conventional punching practice can be employed for these operations.

After the punching operations have been carried out, the ends of the leads 6, 8, 10 are U'd or dished by dies 64 mounted in a recess 66 and in cooperation with suitable punches. Thereafter, the ends of the contact arms 20' on the ends of the outside leads 6, 8 are formed downwardly as shown in FIGS. 4-7. The lower tooling for this initial arm forming operation is mounted on a slide 70 which is disposed in a groove 72 extending from the strip feed path across the front section 74 of the lower die shoe, suitable guides 76 being provided on each side of this slide to guide it accurately towards and away from the strip which is being fed through the die. Slide 70 has a slot or recess 80 in its end adjacent to the front side of the die shoe and a pin 82 is mounted in the slide and extends through this recess. The slide is reciprocated towards and away from the strip by a very slight distance by a camming rod 84 (FIG. 5) which extends from the upper die shoe into recess 80 and which has contoured surfaces as indicated that are effective to drive the slide inwardly during downward movement of the upper die shoe and to retract it during upward movement thereof.

Referring now to FIG. 6, the arms 20' of each blank, as it passed this initial forming station, are moved above a mandrel block 88 which is mounted on one side of the forward end of the slide 70, a recess 86 being provided beneath this mandrel to permit the bending operation described below. After feeding of the strip, the connecting strap portion 12' of the center lead will be supported on the upper surface of block 88 and the end portions of the arms 20' will extend laterally beyond the sides of this block. A clamping block 90 is mounted in the upper die shoe and is resiliently biased downwardly by a spring 92 so that as the upper tooling moves downwardly, the center strap portion 12 and the ends 18 of the leads 6, 10 will be firmly clamped as illustrated in FIG. 7. The laterally projecting contact arm portions 20' are then bent downwardly against the sides of block 88 by a bending tool 92 which surrounds the clamping block 90. At the conclusion of this bending operation then, the arm portions 20 will be bent downwardly as shown at 22' and will be disposed against the sides of the mandrel block 88.

Upon subsequent upward movement of the upper tooling 92 the mandrel block 88 will be retracted from beneath the partially formed leads so that the strip can be fed leftwardly as viewed in FIGS. 6 and 7 for a further forming operation. At this next forming station, which appears on the left in FIGS. 4, 6 and 7, the arms are bent inwardly over a mandrel 96 having curved sides 98. This mandrel block 96 is also mounted on the inner end of the slide 70 and between a pair of forming arms 100 which are disposed in a recess 104 in the slide and are pivoted on a common pivot pin 102. Arms 100 are normally biased apart by a spring 106 and have inner ends which straddle the mandrel block 96 so that when the slide is in its forward or inner position, these arms will be located on each side of the depending contact arms of the leads 6, 10. The opposed surfaces of the forming arms 100 are curved as shown at 108 so that when the arms are moved towards each other and against the sides 98 of the mandrel 96, the contact arms 22 will be inwardly formed as shown on the left in FIG. 7. It should be noted that after this inward bending of the contact arms, they remain spaced apart by a distance which is greater than the width of the connecting strap portion 12 of the center lead.

The forming arms 100 are actuated by a camming punch 114 which is mounted in the upper tooling and which has inclined surfaces 112 that engage the surface 110 of the arms as is apparent from FIGS. 6 and 7 to close the arms 100 against the force of the biasing spring 106. A hold down block or clamping block 116 is mounted in a central passageway in the camming tooling 114 and is resiliently biased downwardly by a spring 118 as indicated to clamp the connecting strap 12 and the ends of the contact leads 18 as is also apparent from FIG. 7.

After the second arm forming operation of FIGS. 6 and 7, the slide 70 is retracted and the mandrel 96 moves from beneath the previously formed contact arms so that the strip can then be fed to subsequent forming stations. Since the contact arms now extend downwardly and beneath the plane of the strip stock, it is necessary to provide a recess or groove 124 for these depending contact arms as indicated in FIG. 8.

Referring again to FIG. 2, further punching operations are carried out at 120 to remove the remaining finger like portion 121 of stock metal between adjacent incipient lead frames. Additionally, the coining operation for forming the sides of the heat sinks may be carried out as shown at 122. Since these are conventional die forming operations, the tooling is not shown in detail although the coining and punching dies are apparent in FIG. 2.

Referring now to FIGS. 8 and 9, the connecting strap section of the central lead 8 is bent at 13 to swing the free ends of all of the leads 6, 8, 10 along an arcuate path downwardly while the inner end portions 18 of the outside leads and the contact arms 20 extending therefrom are swung along an arcuate path upwardly relative to the lower die shoe. This bending operation is carried out by means of a bending tool 132 mounted in the upper die shoe, a recess 126 in one of the die blocks 128 being provided to permit the downward movement of the leads. A forming plate 130 is mounted on the right-hand side of this recess as viewed in FIG. 8 so that its upper surface 130 supports the connecting strap portion of the central lead. The bending tool 132 has a relatively narrow projection 134 on its forwardly facing side which is above the lower surface 133 of this tool. As the bending tool is lowered, the leads are swung downwardly along an arcuate path until the underside of projection 134 moves against the surface of the connecting strap portion of the central lead as shown at FIG. 9. The leads will then extend in a vertical plane and the contact arms will be disposed above the plane of the heat sink as is apparent from FIG. 9.

As shown in FIGS. 10-13, the ends of the contact arms are then bent inwardly and given their final configuration by tooling comprising a slide member 138 and a punch 140 which forms part of the upper tooling. Punch 140 has a channellike recess 142 in its forwardly facing side (FIG. 13), the width of which is substantially equal to the spacing between the outside surfaces of the contact arms. When this punch is lowered, during downward movement the upper die shoe, the slide 138 moves leftwardly as viewed in FIG. 10 and towards the punch. This slide has a recess 144 on its forward end and contoured surfaces 146 which move against the outside surfaces of the contact arms and bend these arms inwardly until their ends 24 are spaced apart by the previously mentioned predetermined distance which is less than the width of the connecting strap 12. Slide 138 has a plate 148 on its upper surface to form the contact arms downwardly and to confine then during the final forming and bending operation. The slide is actuated by a slide block 150 which in turn is mounted in a recess in the lower die shoe and reciprocated by a camming rod 152. This camming rod is mounted in the upper die shoe as previously described with reference to FIG. 5.

Subsequent to the inward forming of the contact arms as illustrated in FIGS. 10-13, the connecting strap is again bent through a 90 .degree.angle at a location 15 adjacent t0 the edge 4 of the heat sink so that the leads are then swung through a 90 .degree.angle along an arcuate path and are disposed in a plane which is parallel to, but above, the plane of the heat sink. After this second bending step, the surface portions of the ends 24 of the contact arms, which have pre-applied solder thereon, will be facing the surface of the heat sink to permit soldering to the chip. The tooling for performing this second bending operation on the connecting strap, FIGS. 14-16 comprises an upper bending tool 157 and a lower bending tool 162 which is integral with a block mounted in a slot 161 in the lower die shoe. A recess in the lower tooling 165 is provided on the left-hand side, as viewed in FIG. 14, of block 160 to provide clearance for the leads as they are swung along an arcuate path as will be apparent from a comparison of FIGS. 14 and 15. In its normal position, the slide 160 is beneath the lower surface of the heat sink and the bending tool 162 is against the underside of the connecting strap portion of the lead frame. The upper bending tool has generally parabolic recesses 157a on its leftwardly facing side (as viewed in FIGS. 15 and 16A) which are separated by a vertically extending rib or projection 158. This projection has laterally extending foot portions 158a on its lower end so that it clamps the connecting strap portion of the lead frame but permits arcuate movement of the formed arms from the positions of FIG. 14 to the positions of FIG. 15.

When the upper bending tool 157 moves downwardly and the slide 160 moves upwardly, a shape right angle bend will be imparted at 15 to the connecting strap portion to bring about the arcuate movement of the leads and to produce the form indicated at 46 in FIG. 3B. The upper bending tool 158 is spring loaded and bottoms on the lead frame before upward movement of slide 160 so that the heat sink and center lead are clamped securedly before commencement of the bending operation.

The bending tool 62 and the block 160 are reciprocated by a lever 170, FIG. 14. A pin extends through a slot 166 in the lower end of block 160 and is received in an open ended slot 168 in the lever 170 which is disposed in a recess 172 in the lower die shoe. THe right-hand end of this lever is pivoted at 174 to a rod 176 which extends above the upper surface of the lower die shoe and which is biased upwardly, as viewed in FIG. 14, by a spring 178 which is received in a recess in the die shoe and which bears against the underside of a nut on the upper end of the rod. The shape of the lever 170 and the dimensions of the recess 172 in which this lever is mounted are such that when the rod 176 is pushed downwardly by a depressor rod 180, the block 160 and the forming tooling portion 158 will be moved upwardly from the position of FIG. 14 to the position of FIG. 15. The rod 180 is mounted in the upper die shoe and has a length such that upward movement of slide 160 takes place after the upper forming tool 158 has bottomed and clamped the heat sink as described above.

Referring now to FIGS. 17 and 18, the connecting strap portion 12 of the center lead is then further formed to increase the bend angles at 13 and 15 until this strap portion extends obliquely between the planes defined by the leads and the heat sink thereby to accurately locate the ends of the contact arms at predetermined locations above the surface of the heat sink. This bending operation is carried out by a slide 184 which is supported on a block 186 across which the strip is fed and which provides a portion of the channel 62 for the heat sink portion of the strip. Slide 184 has an undercut end 190 such that when its pointed end 191 moves rightwardly, as viewed in FIGS. 17 and 18, against the connecting strap portion, a Z-shaped cross sectional configuration of FIG. 18 will be imparted to the lead frame. In order to control the positions of the leads an upper tool 182 is provided which has a recess 188 on its lower end that confines the end portions of the leads 6 and 8 during this operation and maintains all three leads in a horizontal attitude.

The slide 184 extends leftwardly in FIG. 17 and is secured to slide block 192 mounted in a recess in the lower die shoe. Reciprocation is achieved by means of a camming bar 194 mounted in the upper die shoe which is similar to the previously described camming bars.

After completion of the forming operation of FIGS. 17 and 18, the heat sink is substantially in its final form. However, in order to precisely control the dimensions of the finished part, it is desirable to carry out a final sizing operation in which an upper sizing tool 198 moves against the upper surfaces of the leads and further bends the connecting strap 12 until the leads are against the upper surface of a gauge block 196. The precise spacing between the planes of the heat sink and the leads is determined by the dimensions of a projection 200 which depends from this tool member and which moves against the upper surfaces of the leads as shown in FIG. 20.

The operation of this stamping and forming die shown in FIG. 1 will thus be apparent from the step-by-step descriptions of the operations as described above and form the description of the method of the invention presented above with reference to FIGS. 3A and 3B. A significant feature of the invention is the achievement of a lead frame of the general type shown in which the ends of the contact arms are spaced apart by a distance substantially less than the width of the connecting strap and the length of these arms, as measured along the curved sections, is greater than the distance between the two planes of the heat sink and the contact arms. It will be apparent that this result is achieved by bending the contact arms partially, then bending the connecting strap, finally forming the arms, and then finally bending the connecting strap at its secondary locations.

An additional advantage of the invention is that the end portions 24 of the contact arms which are opposed to the heat sink 4 have solder thereon. These arms were formed from the solder striped portion of the metal stock and bent during forming to achieve this effect.

Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments may be made without departing from the scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only.

Claims

I claim:

1. A method of manufacturing lead frames in the form of a continuous strip comprising the steps of:

blanking strip metal stock to form a succession of side-by-side lead frame blanks, each of said blanks comprising a mounting plate portion and three leads extending transversely with respect to the axis of said strip, the center one of said leads being connected to one edge of said mounting plate portion by a connecting strap portion, the outside ones of said leads each having a contact arm on its inner end, said arms extending in opposite directions along the length of said strip, said leads being connected to each other by integral tie bar means,

bending said arms laterally of the plane of said strip,

bending said connecting strap at a location remote from said one edge to swing said leads in one direction along an arcuate path and to orient said leads in a plane extending transversely of the plane of said strip with said arms disposed on one side of said mounting plate portion and with the free ends of said leads disposed on the side opposite to said one side,

further forming said arms substantially to their final configuration, and

bending said connecting strap at a location proximate to said one edge of said mounting plate portion to swing said leads along an arcuate path in a direction opposite to said one direction and orient said leads in a plane which is parallel to, and spaced from, the plane of said strip with said arms between said planes.

2. The method set forth in claim 1 wherein said arms are initially bent partially towards each other.

3. The method set forth in claim 1 wherein said arms are initially bent partially towards each other and during further forming, said arms are bet inwardly until their ends are spaced apart by a distance which is less than the width of said connecting strap portion.

4. The method set forth in claim 3 including the step of further forming said connecting strap portion by bending said strap portion at both said locations until said strap portion extends reversely between said plane and the plane of said strip.

5. A method of manufacturing lead frames in the form of a continuous strip comprising the steps of:

blanking strip metal stock to form a succession of side-by-side lead frame blanks, each of said blanks comprising a mounting plate portion and three leads beside said mounting plate portion, said leads extending transversely of the axis of said strip, the center one of said leads being connected to one edge of said mounting plate portion by a connecting strap portion, the outside ones of said leads having inner ends spaced from said edge and each having a contact arm extending therefrom, said arms extending parallel to the axis of said strip in opposite directions, said leads being connected to each other by integral tie bar means,

bending said arms laterally Of the plane of said strip and partially inwardly towards each other,

bending said connecting strap at a first location remote from said one edge to swing said leads about said location in one direction so that said leads are in a plane extending normally of the plane of said strip with said arms disposed on one side of said mounting plate portion and with the free ends of said leads on the side opposite to said one side,

further forming said arms towards each other until the ends of said arms spaced apart by a distance which is less than the width of said strap,

bending said connecting strap at a second location proximate to said one edge of said mounting plate portion to swing said leads about said second location in a direction opposite to said one direction thereby to orient said leads in a second plane which is parallel to, and spaced from, the plane of said strip, and

further bending said connecting strap portion at said first and second locations to move portions of said leads past said one edge and position said arms at a predetermined location with respect to said mounting plate portion.

6. A method of manufacturing lead frames in the form of a continuous strip, each lead frame being of the type comprising a mounting plate disposed in a first plane and three parallel leads disposed in a second plane which is parallel to, and spaced from, said first plane, said leads being joined to each other by an integral tie bar extending transversely of the axes of said leads, the center one of said leads being joined to one edge of said mounting plate by a connecting strap, which extends between said planes, outside ones of said leads extending over said mounting plate and past said one edge and having contact arms on their ends extending laterally in opposite directions, said arms being reversely bent towards said mounting plate and towards each other, the ends of said arms being spaced-apart by a predetermined distance which is less than the width of said connecting strap and being disposed between said planes, said method comprising the steps of:

blanking strip stock metal to define said mounting plate, said leads, said tie bar, and said connecting strap in said first plane with said leads extending transversely of the length of said strip and with said contact arms extending laterally in opposite directions from said outside leads,

bending said contact arms laterally of said first plane and away from said first and second planes and further bending said arms partially inwardly and towards each other so that the distance between the ends of said arms is greater then the width of said connecting strap,

forming a first right angle bend in said strap at a first location adjacent to said center lead whereby said leads are swung along an arcuate path and are directed away from said first and second planes, and said arms are swung along an arcuate path past said strap and are disposed on the opposite side of said first plane from said free ends of said leads,

further forming said arms inwardly and towards each other until they are spaced apart by said predetermined distance,

forming a second angle bend in said strap at a second location adjacent to said one edge of said mounting plate towards said second plane until said strap extends between said second and first planes whereby said leads and said tie bars are moved along an arcuate path into said second plane and said arms are disposed between said planes and spaced from said mounting plate, and

bending said strap at said first and second locations until said strap extend reversely with reference to said planes and said leads extend in said second plane beyond said one edge.

7. Stamping and forming apparatus for the production of a lead frame of the type comprising a mounting plate disposed in a first plane and three parallel leads disposed in a second plane which is parallel to, and spaced from, said first plane, said leads being joined to each other by an integral tie bar extending transversely of the axes of said leads, the center one of said leads being joined to one edge of said mounting plate by a connecting strap which extends between said planes, the outside ones of said leads extending over said mounting plate and past said one edge and having contact arms on their ends extending laterally in opposite directions, said arms being reversely bent towards said mounting plate and towards each other, the ends of said arms being spaced-apart by a predetermined distance which is less than the width of said connecting strap and being disposed between said planes, said apparatus comprising:

blanking means for blanking strip metal stock to form said mounting plate, said leads, said tie bar and said arms with said leads extending transversely of the length of said strip and with said contact arms extending in opposite directions along the length of said strip,

first arm forming means for bending said arms laterally of the plane of said stock in a first direction and partially inwardly towards each other while leaving a spacing between the tips of said arms which is greater than the width of said connecting strap so that said tips are on each side of, and beyond the sides of said connecting strap,

first strap bending means for bending said connecting strap at a location adjacent to the end of said center lead in said first direction whereby said leads and said tie bar are swung along an arcuate path until said leads extend in said first direction, and said arms are concomitantly swung along an arcuate path past said connecting strap so that the ends of said outside leads extend in a second direction which is opposite to said first direction

second arm forming means for bending said arms further inwardly towards each other until said tips of said arms are spaced apart by a distance which is less than the width of said strap, and

second strap bending means for bending said strap at a location adjacent to said plate in said second direction whereby all of said leads are swung along an arcuate path into said second plane and said connecting strap extends between said planes.